Microstructure and crystallography of textured CoCrTa/Cr recording media

Abstract

Transmission electron microscopy (TEM) has been applied to recording media having a 60 nm CoCrTa film and a 75 nm chromium underlayer, which were DC magnetron-sputtered onto a circumferentially textured NiP/Al substrate. Suitable processing conditions provide in-plane magnetic anisotropy with the preferred direction parallel to the texture lines. This paper focuses on TEM techniques which address the preferred crystallographic orientations purported to be responsible for this important magnetic anisotropy. Elongated probe microdiffraction (EPMD) and standard selected-area diffraction (SAD) patterns from cross-section samples show that the bcc chromium underlayer and the hcp cobalt alloy have strong 〈110〉 and 〈11 2 0〉 out-of-plane growth directions, respectively, which result in in-plane orientations of the Cr 〈110〉 axis and the magnetically easy Co alloy 〈0001〉 c-axis. However, the angular spreads of the growth directions are greater perpendicular to the texture grooves than parallel to them, causing similarly greater out-of-plane components of the Cr 〈110〉 and Co alloy 〈0001〉 axes perpendicular to the texture lines than parallel to them. High-resolution plan-view TEM shows that the Co alloy c-axis has nearly random in-plane orientation. Dark field imaging and EPMD of the plan-view sample show locally altered crystallography near texture lines, but suggest that the change is due in part to the growth orientation tilt, not a dramatic, local, preferred in-plane orientation. Combined, these data suggest that the decreased c-axis in-plane component perpendicular to the texture lines is caused primarily by the 〈11 2 0〉 growth direction following the local grooved surface, not the bulk surface, causing the c-axis to be locally titled out of the bulk film plane near the grooves. This crystallographic difference may have implications upon the observed magnetic anisotropy in these films.